
/* @(#)e_log.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */
#include  <LibConfig.h>
#include  <sys/EfiCdefs.h>
#if defined(LIBM_SCCS) && !defined(lint)
__RCSID("$NetBSD: e_log2.c,v 1.1 2005/07/21 12:55:58 christos Exp $");
#endif

#include "math.h"
#include "math_private.h"

#if defined(_MSC_VER)           /* Handle Microsoft VC++ compiler specifics. */
  // potential divide by 0 -- near line 53, (x-x)/zero is on purpose
  #pragma warning ( disable : 4723 )
#endif

static const double
ln2 = 0.6931471805599452862268,
two54   =  1.80143985094819840000e+16,  /* 43500000 00000000 */
Lg1 = 6.666666666666735130e-01,  /* 3FE55555 55555593 */
Lg2 = 3.999999999940941908e-01,  /* 3FD99999 9997FA04 */
Lg3 = 2.857142874366239149e-01,  /* 3FD24924 94229359 */
Lg4 = 2.222219843214978396e-01,  /* 3FCC71C5 1D8E78AF */
Lg5 = 1.818357216161805012e-01,  /* 3FC74664 96CB03DE */
Lg6 = 1.531383769920937332e-01,  /* 3FC39A09 D078C69F */
Lg7 = 1.479819860511658591e-01;  /* 3FC2F112 DF3E5244 */

static const double zero   =  0.0;

double
__ieee754_log2(double x)
{
  double hfsq,f,s,z,R,w,t1,t2,dk;
  int32_t k,hx,i,j;
  u_int32_t lx;

  EXTRACT_WORDS(hx,lx,x);

  k=0;
  if (hx < 0x00100000) {      /* x < 2**-1022  */
      if (((hx&0x7fffffff)|lx)==0)
    return -two54/zero;   /* log(+-0)=-inf */
      if (hx<0) return (x-x)/zero;  /* log(-#) = NaN */
      k -= 54; x *= two54; /* subnormal number, scale up x */
      GET_HIGH_WORD(hx,x);
  }
  if (hx >= 0x7ff00000) return x+x;
  k += (hx>>20)-1023;
  hx &= 0x000fffff;
  i = (hx+0x95f64)&0x100000;
  SET_HIGH_WORD(x,hx|(i^0x3ff00000)); /* normalize x or x/2 */
  k += (i>>20);
  f = x-1.0;
  dk = (double)k;
  if((0x000fffff&(2+hx))<3) { /* |f| < 2**-20 */
      if (f==zero)
        return (dk);
      R = f*f*(0.5-0.33333333333333333*f);
      return (dk-(R-f)/ln2);
  }
  s = f/(2.0+f);
  z = s*s;
  i = hx-0x6147a;
  w = z*z;
  j = 0x6b851-hx;
  t1= w*(Lg2+w*(Lg4+w*Lg6));
  t2= z*(Lg1+w*(Lg3+w*(Lg5+w*Lg7)));
  i |= j;
  R = t2+t1;
  if(i>0) {
      hfsq=0.5*f*f;
      return (dk-(hfsq-s*(hfsq+R)-f)/ln2);
  } else
    return (dk-((s*(f-R))-f)/ln2);
}
